摘要:

Some of the early techniques for the preparation of carbon films and replicas for the electron microscope are compared with the method of vacuum evaporation developed by the author. The basic techniques for the production of replicas from evaporated carbon are described, and the high resolution obtainable is demonstrated and discussed. Some properties of evaporated carbon replicas are mentioned.Descriptions are given of the carbon replica methods used in metallurgy and some applications are illustrated. Applications of carbon replicas in the following fields of research are also described: microbiology, biology, botany, entomology, chemistry, and industrial applications including the study of fibers.It is concluded that evaporated carbon can be used as the final replica in any multistage replica process, and that it can be applied with advantage in almost every field of research in which the electron microscope is employed.

ISSN:0021-8979    

DOI:10.1063/1.1722278

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A method for suitably etching dislocations in silicon crystals is reported. Using this etch, dislocations in various arrays were observed: low angle boundaries, slip lines, polygonization walls, and bent crystal distributions.

ISSN:0021-8979    

DOI:10.1063/1.1722279

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Young's modulus and internal friction measurements are reported on high‐purity copper following electron bombardment. The modulus is observed to rise rapidly with electron flux reaching an early saturation followed by a slow decrease. The rapid saturation is attributed to dislocation pinning. The rate of saturation is temperature dependent in the range from −195°C to about 0°C suggesting defect migration at low temperatures. The slow decrease is attributed to a ``bulk effect'' due to interstitial‐vacancy pairs.

ISSN:0021-8979    

DOI:10.1063/1.1722280

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Four‐electrode conductivity measurements over the temperature range from 500 to 1000°K have been made on clear BaO single crystals and on crystals colored blue by excess barium densities between 0.3 and 6×1017per cc. Barium was introduced into the crystals by heating in a barium atmosphere and the excess barium densities were computed by the Smakula formula from the 2.0‐ev optical absorption band following the method of Sproull, Bever, and Libowitz. The conductivities of the clear crystals attain values of 10−4mho/cm at 1000°K whereas the blue crystals show a conductivity maximum of about 1 mho/cm at about 900°K. The assumption of an electron mobility of 5 cm2/volt sec leads to an agreement of the saturation electron density and the excess barium density to within a factor of three.

ISSN:0021-8979    

DOI:10.1063/1.1722281

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The growth of the luminous area of a high current discharge in an electronic xenon‐filled flashtube has been studied by means of a sequence of timed short‐exposure photographs taken with a magneto‐optic shutter. Electrical measurements show that the tube conductance is approximately proportional to the luminous area of the arc channel. The ionized gas has a volume conductivity of about 90 mho/cm averaged over the luminous path during the buildup for the conditions investigated.

ISSN:0021-8979    

DOI:10.1063/1.1722282

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The diffusion of aluminum into silicon has been reinvestigated to clear up certain discrepancies in the existing aluminum data. The diffusion constants found in this work are in good agreement with those determined by Fuller and Ditzenberger and an order of magnitude less than those reported in another investigation. Aluminum solid solubilities in the neighborhood of 1019atoms/cm3have been found over the 1200 to 1400°C temperature range. These concentrations are several orders of magnitude larger than those reported in other aluminum diffusion investigations. Thep‐njunction penetrations and transition capacitances of the diffused samples were used to determine diffusivities and solid solubilities.

ISSN:0021-8979    

DOI:10.1063/1.1722283

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

Expressions for the attenuation of sound waves in a standard linear viscoelastic body have been derived and have been applied to the attenuation due to the thermoelastic effect.The thermoelastic attenuation for sound waves has been computed for single crystals and polycrystalline materials under application of the high‐frequency approximation of sound propagation. For single crystals the attenuation in the main propagation directions have been computed explicitly for cubic and hexagonal crystals taking into account the anisotropy of the elastic properties and thermal expansion.Comparison with experiments in the megacycle region shows that the attenuation caused by heat flow between the grains of a polycrystalline specimen is usually overpowered by scattering at the grain structure. Also the computed attenuation caused by heat flow between the regions of compressions and rarefaction of the wave is for many materials much smaller than the measured values.For single crystals of certain metals, however, the computed and the measured values have the same order of magnitude. It can be shown that in these cases the attenuation is composed of a thermoelastic component and of a component resulting from dislocations. In zinc the two components can be separated experimentally and the agreement between the measured and the computed thermoelastic damping is very good.

ISSN:0021-8979    

DOI:10.1063/1.1722284

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

A technique is described whereby bulk carrier lifetimes in semiconductors can be measured over a wide range of injection level without making any electrical connections to the sample. The excess carriers are created by visible light and their distribution is measured by absorption of infrared radiation. The most important advantage of this technique is that the electric field term can be neglected in the continuity equation which describes the carrier distribution and the diffusion length can thus be determined directly. It appears that this technique may be used even in the presence of trapping. Some measurements are described for germanium where it is found that the carrier lifetime may increase or decrease with injection level. This is consistent with the Hall‐Shockley‐Read theory of carrier recombination.

ISSN:0021-8979    

DOI:10.1063/1.1722285

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The variance of narrow band noise plus c.w. signal after detection and integration over a finite time interval is derived. The problem is solved for Ideal, Gaussian, and HighQSingle Tuned filters with square law and linear detection, the latter for large predetection signal‐to‐noise ratio. In addition to these filters the analysis is carried through for a model which considers the envelope of narrow band noise plus signal as a function which is constant for intervals of duration equal to the reciprocal of the noise band width and statistically independent in different intervals. Graphs of the mean square deviation divided by the mean power for noise alone are given for all filters and the model, with square law detection and predetection signal‐to‐noise ratios 0, 0.5, 1, 2.

ISSN:0021-8979    

DOI:10.1063/1.1722286

出版商:AIP    

年代:1956

数据来源: AIP

摘要:

The magnetic technique of particle size measurement based on the work of Elmore consists of a comparison of a modified Langevin curve with the observed magnetization curve for an appropriate system of ferromagnetic particles. The average magnetic moment per particle is obtained from this analysis, and the average particle size is thus determined. The prediction by Ne´el of thermal relaxation in single‐domain ferromagnetic particles broadens the range of applicability of the granulometry method, with special emphasis on the size range from 20 A to about 100 A. A possible objection to the method, arising from evidence for an abnormal temperature dependence of the saturation magnetization of very small magnetic particles, is re‐examined experimentally and found to be invalid. Several examples are presented that demonstrate the predicted thermal relaxation and that point to a wide utilization of the granulometry technique.

ISSN:0021-8979    

DOI:10.1063/1.1722287

出版商:AIP    

年代:1956

数据来源: AIP